1. Field of the Invention
The present invention relates to a substrate holding apparatus and an exposure apparatus including the substrate holding apparatus, and more particularly, to a substrate holding apparatus, which is used for holding a substrate when transferring a mask pattern onto the substrate in a lithography process for manufacturing devices such as a semiconductor device, a liquid crystal display device, a plasma display device and a thin film magnetic head, and to an exposure apparatus including the substrate holding apparatus.
2. Description of the Related Art
In the case of manufacturing a semiconductor device or the like, in order to transfer a reticule pattern image used as a mask to each shot area on a wafer (or a glass plate, etc.) which is used as a substrate onto which a resist is applied, a full field exposure type, such as a step-and-repeat type, exposure apparatus, and a scanning exposure type, such as a step-and-scan type, exposure apparatus are used. In the aforesaid exposure apparatuses, a wafer is held on a wafer holder by vacuum chucking, electrostatic chucking or/the like, and the wafer holder is fixed on a coarsely and finely movable wafer stage.
A conventional wafer holder includes, as disclosed, for example, in Japanese Unexamined Patent Application Publication No.1-129438, a large number of pins arranged like a square lattice, and a suction portion for sucking the gas from a suction hole between these pins. In a state in which the wafer is placed on the large number of pins, the gas between the wafer and the wafer holder is exhausted by the suction portion, and thereby, the wafer has been chucked and held. Moreover, in order to prevent the wafer from being electrically charged, the entire surface of the wafer holder is coated with a conductive material, and further, earth connection is carried out with respect to the back side of the wafer holder.
As described above, in the conventional wafer holder, the wafer is placed on the plurality of pins arranged, for example, like a square lattice, and the wafer is held by vacuum chucking or the like. However, a deformation (warp, etc.) is locally generated in the wafer by the vacuum chucking or the like. When the deformation is increased to a range of the depth of focus of a projection optical system, a resolution at that portion is lowered; for this reason, preferable exposure cannot be made locally in some shot areas on the wafer.
In order to suppress the above wafer deformation due to vacuum chucking or the like, there is a need of making fine intervals between pins arranged for supporting the wafer or weakening a suction force. However, when the suction force is simply weakened, there is a possibility such that a shift occurs in wafer alignment during acceleration period and deceleration period of step movement. On the other hand, when the intervals between the arranged pins are made fine, a contact rate of the wafer with the wafer holder increases, and there is a high possibility such that foreign matters are held between the back side of wafer and the wafer holder. For this reason, a problem arises such that a flatness of wafer is reduced.
Moreover, in the case where the wafer holder is formed of a material having a low coefficient of thermal expansion, when the surface of the wafer holder is coated with an anti-electrical charging material, an internal stress is generated due to a difference in the coefficients of thermal expansion between the anti-electrical charging material and the material forming the wafer holder. As a result, there is a possibility such that the anti-electrical charging material cracks and peels off. For this reason, it is difficult to thick coat the anti-charging material to the surface of the wafer holder. Therefore, after the surface of the wafer holder is coated with an anti-electronic charging material, in order to improve a flatness of the contact surface of the wafer holder with the wafer, it is difficult to carry out polishing and the like with respect to the contact surface (coating surface). As a result, a problem arises such that micro unevenness remains in the contact surface.
In addition, in a manufacture of semiconductor device or the like, an improvement of throughput has been demanded. However, in a conventional exposure apparatus, a wafer is first placed on a wafer bolder, and thereafter, the exhaust (suction) of the gas is started by a vacuum pump for chucking and holding the wafer. For this reason, it takes a long time until a force required for holding the wafer is increased up to a desired value. Further, in the case of carrying out the wafer from the wafer holder for wafer exchange, conventionally, a valve communicating with a gas having an atmospheric pressure is simply opened in the case of stopping the suction by the vacuum pump. For this reason, it takes a long time until the suction force of wafer is lost. Therefore, in the conventional wafer holder, it takes a time to load and unload the wafer; for this reason, this is a factor of faults in improvement of throughput of exposure process.
The present invention has been made in view of the above problems in the prior art. It is, therefore, a first object of the present invention to provide a substrate holding apparatus, which can reduce a deformation in the case of chucking a substrate such as a wafer with respect to a contact area of the substrate with the wafer holder.
Further, a second object of the present invention is to provide a substrate holding apparatus, which is constructed in a manner that an area including a contact surface with the substrate is coated with, for example, an anti-electronic charging material, and can prevent a crack and the like of the anti-electronic charging material.
Further, a third object of the present invention is to provide a substrate holding apparatus, which can carry out a substrate chucking start operation or substrate chucking release operation at a high speed so that throughput is improved.
Further, another object of the present invention is to provide an exposure apparatus including the aforesaid substrate holding apparatus.
According to a first aspect of the present invention, there is provided a substrate holding apparatus which holds a flat-like substrate, comprising:
a base member; and
a plurality of projecting support members disposed on said base member such that the supporting members are arranged like a triangular lattice and distal end portions thereof are positioned on substantially the same plane, wherein
the substrate is to be placed on the plurality of support members.
Like the substrate holding apparatus according to the first aspect of the present invention, in a case where the plurality of support members which are to contact the substrate are arranged like a triangular lattice, the following effect is obtained. More specifically, as compared with the case where these plural support members are arranged like a rectangular lattice, an interval between the plural support members and the position of the center of gravity is shortened with respect to a density of the support members (area contacting with the substrate), and a deformation of the substrate is reduced. Therefore, according to the first aspect of the present invention, the following effect is obtained. More specifically, when a probability that foreign/matters are held between the substrate and the plurality of support members is the same as the conventional case, it is possible to reduce a deformation of the substrate in the case where the substrate is chucked by electrostatic chucking or vacuum chucking, and thus, to prevent a flatness of the substrate from becoming worse. As a result, in a case where the substrate holding apparatus is applied to an exposure apparatus, a mask pattern can be transferred on the entire surface of the substrate at a high resolution.
In this case, it is preferable to provide a suction mechanism which sucks the substrate placed on the plurality of support members toward the base member side. By the suction, it is possible to prevent the substrate from being shifted laterally in the case where the substrate holder is moved.
Moreover, in a case where the suction mechanism is constructed as a vacuum chucking type, an example of the suction mechanism includes a ring-like closed protrusion formed on the base member so as to surround the plurality of support members, and a gas suction portion which sucks gas inside the protrusion. In the above construction, in order to reduce a probability that foreign matters are held between the protrusion and the substrate, it is preferable that the upper surface of the protrusion is provided with a plurality of projecting support members of an extremely lower step height (of a small leak) for holding the Substrate.
In these cases, it is preferable that a suction mechanism is provided which sucks the substrate placed on the plurality of support members toward the base member side, and the plurality of support members are disposed like a lattice of equilateral triangles each having one side with a length xe2x80x9caxe2x80x9d [m], and when a suction force per unit length is set as xe2x80x9cpxe2x80x9d [N/m] in the case of sucking the substrate toward the base member side, an allowable deformation amount is set as xe2x80x9cxcex4maxxe2x80x9d [m] in the case of sucking the substrate, Young""s modulus E of the substrate is set as E [Pa], and a thickness of the substrate is set as xe2x80x9ctxe2x80x9d [m], the length xe2x80x9caxe2x80x9d of the equilateral triangle and the suction force xe2x80x9cpxe2x80x9d satisfy the following condition (1).
pxc2x7a4xe2x89xa618xc2x7Exc2x7t3xc2x7xcex4maxxe2x80x83xe2x80x83(1) 
By satisfying this condition, it is possible to suppress the deformation of the substrate due to the suction equal to or less than the allowable deformation amount of xe2x80x9cxcex4maxxe2x80x9d.
Next, according to a second aspect of the present invention, there is provided a substrate holding apparatus which holds a flat-like substrate, comprising:
a base member; and
a plurality of projecting support members disposed on the base member such that distal end portions thereof are positioned on substantially the same plane, wherein
a conductive material is coated on a predetermined area including a contact surface of the support member with the substrate, and an area which is not coated with the conductive material is partially formed in the predetermined area. It is preferable that the area is formed into a shape of slit.
According to the substrate holding apparatus according to the second aspect of the present invention, the area which is not coated with the conductive material (anti-electronic charging material) is formed into the slit-like shape, for example. Thus, it is possible to prevent the conductive material from cracking and peeling off due to a difference in coefficients of thermal expansion between the material forming the base member and the support member and the conductive material. As a result, the conductive material can be coated thick to some degree, and therefore, the contact surface with the substrate can be subjected to machining after the conductive material is coated. Accordingly, it is possible to secure a excellent flatness of the contact surface with the substrate, and thus, to secure a excellent flatness of the substrate.
In this case, it is preferable that the base member and the plurality of support members are made of a non-conductive material having a low thermal expansion coefficient. This is because of reducing expansion and contraction by a change of temperature. An example of the conductive material is titanium nitride or titanium carbide.
According to a third aspect of the present invention, there is provided a substrate holding apparatus which holds a flat-like substrate, comprising:
a base member having a plurality of projecting support members, distal end portions thereof which are to contact the substrate being positioned on substantially the same plane, the base member having a coating on a surface thereof except for a part of a mounting surface for the substrate, and the part being different from a contact surface with the substrate, and
a suction mechanism which is connected to the base member and which sucks gas between the substrate and the base member.
Next, according to a fourth aspect of the present invention provides a substrate holding apparatus which holds a flat-like substrate, comprising:
a base member;
a plurality of projecting support members which are disposed on the base member such that distal end portions thereof are positioned on substantially the same plane,
a ring-like closed protrusion formed on the based member so as to surround the plurality of support members; and
a gas suction portion which sucks gas inside the protrusion, wherein
a suction force after the substrate is placed on the plurality of support members is set weaker than a suction force when the substrate is placed on the plurality of support members.
According to the substrate holding apparatus according to the fourth aspect of the present invention, the suction force in the chucking start operation when the substrate is placed on the plurality of support members is set larger than the suction force after the substrate is placed (e.g., processing such as exposure or the like). Therefore, it is possible to shorten a time until a desired chucking force is obtained from the chucking start, and to improve a throughput of exposure process in the case where the substrate holding apparatus is applied to an exposure apparatus. Moreover, the suction force in processing is set to a degree such that no positional shift of substrate is generated; therefore, it is possible to reduce a deformation of the substrate by chucking to the minimum.
In this case, when the substrate is taken off from the plurality of support members, it is preferable to provide an air supply portion which blows gas into the inside of the ring-like projected portion. By doing so, the chucking release operation of the substrate can be carried out at a higher speed.
Further, according to a fifth aspect of the present invention, there is provided an exposure apparatus which exposes a second object with an exposure beam via a first object, and which includes the substrate holding apparatus according to any one of the first to third aspects of the present invention, wherein the substrate holding apparatus holds the second object as the substrate. According to the fifth aspect of the present invention, because it includes the substrate holding apparatus according any one of the first to third aspects of the present invention, it is possible to secure an excellent flatness of the substrate without reducing the chucking force for the substrate, and to manufacture a high function device at a high throughput.
According to the sixth aspect of the present invention, there is provided an exposure apparatus which illuminates a first object with an exposure beam, and exposes a second object by the exposure beam via the first object, comprising:
a holder having a plurality of projecting support members disposed like a triangular lattice such that distal end portions thereof which are to contact the second object are positioned on substantially the same plane, and
a stage system including a movable body in which the holder is provided.
According to a seventh aspect of the present invention, there is provided an exposure apparatus which illuminates a first object with an exposure beam, and exposes a second object with the exposure beam via the first object, comprising:
a holder having a plurality of projecting support members with distal end portions thereof which are to contact the second object are positioned on substantially the same plane, the holder being coated on a surface thereof except for-a part of a mounting surface for the second object and the part being different from a contact surface with the second object, and
a stage system including a movable body in which the holder is provided.
According to an eighth aspect of the present invention, there is provided an exposure apparatus which illuminates a first object with an exposure beam, and exposes a second object by the exposure beam via the first object, comprising:
a holder having a plurality of projecting support members with distal end portions thereof which are to contact the second object being positioned on substantially the same plane, and
a suction mechanism which is connected to the holder and which sets a suction force after the second object is placed to be weaker than a suction force when the second object is placed on the plurality of support members.